Internal electrode and assembly method for electrochemical cells

ABSTRACT

An electrode for an alkali metal electrochemical cell comprising a unitary conductive body having a pair of wing-like sections joined by an intermediate web section. The cell anode or cathode parts are in contact with corresponding ones of the electrode wing sections, and the electrode web section is adapted to be placed in contact with the cell conductive casing. This results in a case negative or case positive electrical configuration depending upon whether the anode or cathode parts are in contact with the electrode wing sections. In forming an anode-cathode sub-assembly the anode or cathode parts are joined to the electrode wing sections and then the electrode wing sections are folded relative to the electrode web section and toward each other in a manner to place the anode and cathode parts in operative contact with each other. The internal electrode and assembly method advantageously require only the electrode intermediate web section to be bonded to the cell casing thereby allowing the cell to be assembled in a relatively quick and easy manner.

This is a divisional of copending application(s) Ser. No. 07/757,252filed on Sep. 10, 1991, now U.S. Pat. No. 5,250,373.

BACKGROUND OF THE INVENTION

This invention relates to the art of electrochemical cells, and moreparticularly to a new and improved internal electrode and assemblymethod for alkali metal/solid cathode and alkali metal/oxyhalide cells.

The recent growth in small-sized electronic devices has requiredelectrochemical cells having high energy density and current deliverycapability. As a result of this need alkali metal/solid cathode andalkali metal/oxyhalide cells have been developed wherein the anodetypically is lithium and the electrolyte is either solid or liquid. Indesigning such cells it has been found to be advantageous to provide acasing of stainless steel or like conductive metal in operative contactwith either the anode or the cathode to provide, respectively, a casenegative or case positive electrical configuration. However, thisnecessitates welding or otherwise bonding components of the anode orcathode to the casing which can add difficulty and time to the assemblyoperation.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of this invention to provide a newand improved internal electrode and assembly method for alkalimetal/solid cathode cells and for alkali metal/oxyhalide cells.

It is a further object of this invention to provide such an electrodeand assembly method for cells having a conductive casing in a casepositive or case negative electrical configuration.

It is a more particular object of this invention to provide such anelectrode and assembly method which avoids the necessity of bondingcomponents of the cell anode or cathode to the cell casing.

It is a more particular object of this invention to provide such anelectrode and assembly method which enables the cell in which it iscontained to be manufactured in a relatively quick and easy manner.

The present invention provides an electrode for an alkali metalelectrochemical cell comprising a unitary conductive body having a pairof wing-like sections joined by an intermediate web section. The cellanode or cathode parts are in contact with corresponding ones of theelectrode wing sections, and the electrode web section is adapted to beplaced in contact with the cell conductive casing. This results in acase negative or case positive electrical configuration depending uponwhether the anode or cathode parts are in contact with the electrodewing sections. In forming an anode-cathode sub-assembly the anode orcathode parts are joined to the electrode wing sections and then theelectrode wing sections are folded relative to the electrode web sectionand toward each other in a manner to place the anode and cathode partsin operative contact with each other.

The foregoing and additional advantages and characterizing features ofthe present invention will become clearly apparent upon a reading of theensuing detailed description together with the included drawing wherein:

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a perspective view of an electrochemical cell including aninternal electrode according to the present invention;

FIG. 2 is an enlarged sectional view taken about on line 2--2 in FIG. 1;

FIG. 3 is an enlarged sectional view taken about on line 3--3 in FIG. 1;

FIG. 4 is a sectional view taken about on line 4--4 in FIG. 3;

FIG. 5 is a fragmentary sectional view taken about on line 5--5 in FIG.3;

FIG. 6 is a fragmentary sectional view taken about on line 6--6 in FIG.3;

FIG. 7 is a fragmentary sectional view taken about on line 7--7 in FIG.3;

FIG. 8 is a plan view of the anode assembly in the cell of FIGS. 1-7;

FIG. 9 is an opposite plan view of the anode assembly of FIG. 8;

FIG. 10 is an elevational view taken about on line 10--10 in FIG. 8 andillustrating a step in the method of the present invention;

FIG. 11 is a developed view illustrating the method of making ananode-cathode assembly according to the method of the present invention;and

FIG. 12 is a sectional view similar to FIG. 2 illustrating analternative embodiment of the electrode of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring now to FIG. 1, there is shown an alkali metal/solid cathodeelectrochemical cell 10 including an internal electrode according to thepresent invention. The internal electrode and other cell components arecontained within a casing 12 of metal such as stainless steel includingspaced-apart sidewalls 14,16 joined by curved end walls 18,20 and acurved bottom wall 22. The open top of casing 12 is closed by a lid 24.

The internal electrode of the present invention can be used with alkalimetal/solid cathode or alkali metal/oxyhalide electrochemical cells ofboth solid cathode and liquid electrolyte types. In the solid cathodetype, for example a lithium-solid cathode cell, a solid cathode materialsuch as silver vanadium oxide is contained within casing 12 andsurrounded by a separator. A lithium anode also is in the casing.External cell electrical connection is provided by a terminal lead 28and by a contact region comprising lid 24 or the entire conductivecasing 12 which is insulated from lead 28. In the liquidcathode/electrolyte type, for example a lithium-oxyhalide cell, liquidelectrolyte fills the casing interior and is in operative contact withthe anode and with a cathode element comprising a carbon body having acathode current collector embedded therein. A separator is employedbetween the anode and the carbon cathode. For a more detaileddescription of such a liquid electrolyte cell reference may be made toU.S. Pat. No. 4,440,453 issued Jan. 20, 1981 and entitled "High EnergyDensity Battery System" and assigned to the assignee of the presentinvention, the disclosure of which is hereby incorporated by reference.

Referring now to FIG. 2, the cell 10 according to this embodiment of thepresent invention is of the liquid electrolyte type comprising a cathodein the form of a body 36 of cathode material which will be described indetail presently. A cathode current collector 38 embedded in body 36 isjoined to lead 28 which extends through lid 24 and is electricallyinsulated from the same in a manner which will be described. Cathodebody 36 has a pair of oppositely directed surfaces 40 and 42 which areoperatively associated with a pair of lithium anode elements or plates44 and 46, respectively. In particular, lithium anode element 44 is inoperative contact with cathode body surface 40 through a thin sheet ofseparator material 50. Similarly, lithium anode element 46 is inoperative contact with cathode body surface 42 through a thin body ofseparator material 52 which surrounds the cathode pellet.

In accordance with the present invention, cell 10 includes an electrodegenerally designated 60 comprising a unitary body having a pair ofwing-like sections 62 and 64 joined by an intermediate web section 66.Lithium anode elements 44 and 46 are in contact with and carried bycorresponding ones of the electrode wing sections 62 and 64,respectively. In particular, lithium elements 44 and 46 are pressurebonded to electrode wing sections 62 and 64, respectively, in a mannerwhich will be described in detail presently. The electrode web section66 is in operative contact with casing 12, in particular being joined tothe underside of lid 24.

Cell 10 is completed by a liquid electrolyte 70 in casing 10. Lead 28 isthe positive electrical terminal, being connected to the cathode. Withelectrode 60 being in operative contact with the conductive casing 12,the cell 10 of this embodiment of the present invention is in a casenegative electrical configuration.

The electrode assembly of the present invention is shown in furtherdetail in FIGS. 8 and 9. Electrode 60 is fabricated from a thin sheet ofmetal, preferably nickel, and wing-like sections 62 and 64 are of meshformation to facilitate adherence to the lithium anode elements 44 and46, respectively. Each wing section has a length greater than the lengthof the web section, and the widths of the wing sections are equal. Oneend of each wing section, the left end as viewed in FIG. 8, extendsbeyond the corresponding end of the web a distance greater than that bywhich the opposite end extends to accommodate other cell components aswill be described. The central web section 66 is provided with extendingtabs 74 and 76 terminating in semi-circular cutouts 78 and 80,respectively, at opposite ends thereof to facilitate assembly in thecell as will be described. Web section 66 also is provided withlongitudinally spaced, laterally extending slots or rectangular cutouts84 which are separated into three groups divided by longitudinallyextending slots 86. The junctions between the web section 66 and thetwo-wing like sections 62 and 64 are provided with elongated rectangularopenings or slots 90 and 92, respectively, to facilitate folding duringassembly which will be described.

The lithium anode elements 44 and 46 are of the same shape orconfiguration as the corresponding electrode wing sections 62 and 64,respectively. In addition, each lithium anode element 44 and 46 is ofslightly larger size or surface area as compared to the correspondingelectrode wing section 62 and 64 so as to define a marginal orperipheral extension or border surrounding the periphery of the wingsection. Thus, the length of each of the lithium anode elements 44 and46 is slightly greater than the length of the corresponding electrodewing section 62 and 64. The width of each lithium anode element 44 and46 is of an extent such that it terminates slightly beyond the long edgeof the corresponding wing section 62 and 64, and at the opposite sideterminates a short distance form electrode web section 66 in an edgewhich is located substantially midway along the corresponding opening 90and 92. Each of the lithium anode elements 44 and 46 is pressure bondedto the corresponding electrode wing section 62 and 64 in a manner wellknown to those skilled in the art, this being facilitated by the meshformation of the wing sections 62,64 in a known manner. Thus, lithiumanode elements 44 and 46 are joined to electrode wing sections 62 and 64so as to be in contact with and carried by the wing sections 62 and 64and spaced from the web section 66. In the cell shown, the electrodeassembly is completed by a pair of rectangular lithium elements orsheets 96 and 98 on sides of the electrode wing sections 62 and 64opposite the lithium plates 44 and 46, respectively. Lithium sheets96,98 are optional and may be provided to insure long-term contactbetween the anode and anode current collector. Sheets 96,98 are ofsmaller thickness and smaller surface area as compared to the lithiumelements 44,46 and are located slightly offset longitudinally from themid-points of the electrode wing sections 62 and 64.

FIGS. 10 and 11 illustrate the method of forming an anode-cathodesubassembly according to the present invention. The electrode assemblyof FIGS. 8 and 9 is provided and is shown in solid lines in FIG. 10. Theelectrode wing sections 62,64 with anode lithium elements 44,46 andlithium sheets 96,98 carried thereby are folded relative to web section66 and toward each other as shown in broken lines in FIG. 10 in thedirection of arrows 99,100. They are folded in a manner to place thelithium anode parts in operative contact with the cathode to provide ananode-cathode subassembly. The method is further illustrated in FIG. 11wherein the electrode wing sections 62,64 are shown in positionintermediate to the final position to which they are folded to place thelithium anode parts 44,46 in operative contact with the cathode body 36.The relative positions between the separator sheets 50 and 52 and thelithium anode elements 44 and 46 is shown in FIG. 11 as well as thelocation of shielding and insulating sheets 102 and 104, respectively,between electrode web section 66 and cathode body 36 as will bedescribed. FIG. 11 also illustrates the location of a header assembly106 relative to the electrode web section 66, the terminal lead 28extending through the header assembly for making connection to cathodecurrent collector 38 in a manner which will be described.

A completed cell including the anode-cathode sub-assembly illustrated inFIG. 11 is shown in FIGS. 3-7. Cathode current collector 38 is providedwith a tab 120 welded thereto and extending outwardly therefrom whereinit is welded to one end of a coupling element 124, the other end ofwhich is welded to the inner end of terminal lead 28. Lead 28 is fixedrelative to lid 24 by a generally cylindrical ferrule element 130 whichis fitted at one end to an opening 132 in lid 24 as shown in FIG. 6 andsecured thereto such as by welding. The space between lead 28 andferrule 130 is filled by a glass seal 136 which extends along the majorportion of the length of element 130. Glass seal 136 insulates lead 28electrically from lid 24. An elastomeric seal member 138 can be providedwhich is fitted in element 130 and faces toward the interior of the cellcasing as shown in FIG. 6. Glass seal 136 normally is resistant tocorrosion from the cell chemicals and therefore seal 138 is optional.The welding shield 102 in the form of an elongated strip is locatedadjacent the inner surface of lid 24 and is of suitable material such asmica. The insulator strip 104 of suitable material such as Tefzel islocated between welding shield 102 and the remainder of the cell. Lid 24is provided with a fill opening 140 shown in FIG. 7 adjacent theopposite end in a known manner, and a fill ferrule 148 is welded in theportion of opening 140 adjacent the inner surface of lid 24 as shown. Aninsulator 150 in the form of a cap of suitable material such as Tefzelcan be provided to cover the portion of ferrule 130 below lid 24 asshown in FIG. 6. Similarly, an insulator 152 can be associated withferrule 148. In particular, insulator 152 is of suitable material suchas Tefzel and includes a cap portion 154 for covering the portion offerrule 148 extending below lid 24 and a strap portion 156 extendingfrom cap 154 and along strip 104.

The cell of FIGS. 3-7 is assembled in the following manner. First, theanode assembly as shown in FIG. 10 is provided. Next, ferrule 130 iswelded to lid 24 in opening 132 and, similarly, ferrule 148 is welded tolid 24 in opening 140. Pin 28 is fixed in ferrule 130 by means of glassseal 136, and elastomeric seal 138 if used is put in place. Next, strips102,104 are positioned against the lower surface of lid 24 and insulatorcap 150 is placed on ferrule 130. After that, strips 102,104 are pivotedabout their connection to element 130 and the electrode web section 66is welded to lid 24 at the locations designated 160 in FIG. 4. Thestrips 102,104 are then pivoted back to overlie the electrode websection 66. Next, cathode body 36 containing current collector 38 isbrought into proximity, and the electrode wing sections 62,64 are foldedtoward the cathode body 36 with separators 50,52 therebetween and theentire assembly is placed in the casing 12 with lid 24 closing theopening thereof. Lid 24 is then welded to the periphery of casing 12,and the mica shield 102 protects the remainder of the cell componentsfrom the heat during such welding. After liquid electrolyte isintroduced to the interior of the casing through the fill opening 140,the opening is sealed first by the inner plug 162 of suitable materialsuch as plastic or metal and then by the outer seal 164 which is weldedto lid 24 in opening 140. Insulator 152 serves as a heat shield orbarrier to protect the cell separators 50,52 when seal 164 is welded inplace. The strap portion 56 of insulator 152 serves to space the cathodeassembly from lid 24.

With the internal electrode 60 and assembly method according to thepresent invention, advantageously only the electrode web section isbonded to the cell casing, i.e. to lid 24, and bonding of components ofthe anode or cathode to the cell casing is avoided. This, in turn,enables the cell to be assembled in a relatively quick and easy manner.

By way of example, in an illustrative cell, the material of cathode body36 is a silver vanadium oxide cathode material as described in U.S. Pat.Nos. 4,310,609 issued Jan. 12, 1982 and 4,391,729 issued Jul. 5, 1983,both assigned to the assignee of the present invention, the disclosuresof which are hereby incorporated by reference. Cathode current collector38 is of titanium, separators 50,52 are of polypropylene, electrolyte 70is a 1.0 Molar solution of lithium hexafluoroarsenate prepared bydissolving lithium hexafluoroarsenate in equal quantities of DEM (GYLME)and propylene carbonate, pin 28 is of molybdenum, coupling element 124is of titanium, glass seal 136 is of TA-23 Hermetic sealing glass, andferrules 130 and 148 together with plug 164 and fill ferrule are ofstainless steel.

FIG. 12 illustrates an alternative embodiment of the internal electrodeof the present invention as it would appear in a completed, assembledcell. Components in the embodiment of FIG. 12 identical to those in theembodiment of FIG. 1-11 are identified by the same reference numeralsprovided with a prime designation. In this embodiment, the electrode websection 66' is shaped to conform to the shape of the inner surface ofcasing 12' at a location generally opposite lid 24'. In particular,electrode web section 66' is shaped to conform to the inner surface ofthe casing curved bottom wall 22'. The anode-cathode sub-assembly isformed in a manner similar to that illustrated in FIGS. 8-11. In theassembly of the cell, cathode current collector 38' is connected to pin28' and the insulator arrangement is provided in a manner similar tothat described in connection with FIGS. 3-5, and the anode-cathodesub-assembly is inserted in casing 12' with the curved electrode webportion 66' placed in contact with the curved inner surface of casingbottom 22'. If desired, web portion 66' can be bonded such as by weldingto the inner surface of bottom wall 22'. The remainder of the assemblingof the cell of FIG. 12, including welding lid 24' in place, introducingelectrolyte 70' and closing the fill opening in lid 24' is performed ina manner similar to that described in connection with the embodiment ofFIGS. 1-11. The completed cell is in a case negative electricalconfiguration.

The internal electrode of the present invention can also be employed ina case positive electrical configuration. In particular, in theembodiments of FIGS. 1-12, with the lithium anode elements contactingthe internal electrode 60, which, in turn, contacts the conductive cellcasing 12, the cell is in a case negative electrical configuration. Acase positive electrical configuration is provided by placing thecathode parts in contact with the internal electrode 60 which, in turn,is in contact with the conductive cell casing 12. In particular, andreferring to the anode-cathode subassembly of FIG. 11, a case positiveelectrical configuration is provided by replacing lithium anode elements44,46 with cathode current collector elements on the electrode wingsections 62,64. The lithium sheets 96,98 also would be removed. Cathodebody 36 and current collector 38 would be replaced by a pair of lithiumanode elements or plates sandwiched together and against an anodecurrent collector which, in turn, is connected to pin 28 and insulatedfrom lid 24. With the cathode parts in contact with electrode wingsections 62,64 and with the electrode web section 66 in contact with thecell casing, a cell is provided in a case positive electricalconfiguration.

It is therefore apparent that the present invention accomplishes itsintended objects. While embodiments of the present invention have beendescribed in detail, that is for the purpose of illustration, notlimitation.

What is claimed is:
 1. A method of making an anode assembly for analkali metal/solid cathode electrochemical cell having a conductivecasing comprising the steps of:a) providing an electrode in the form ofa unitary body having a pair of wing-like sections joined by anintermediate web section; b) providing an alkali metal anode comprisingtwo parts; and c) joining said anode parts to corresponding ones of saidelectrode wing sections so as to be in contact with and carried therebyand spaced apart by said web section so that said web section can beplaced in contact with said conductive casing to provide a case negativeelectrical configuration.
 2. A method according to claim 1, furtherincluding the step of folding said electrode wing sections relative tosaid web section and toward each other in a manner to place said anodeparts in operative contact with a cathode to provide an anode-cathodesub-assembly.
 3. A method of making an alkali metal/solid cathodeelectrochemical cell comprising the steps of:a) providing a metal casinghaving an opening at one end; b) providing an electrode in the form of aunitary body having a pair of wing-like sections joined by anintermediate web section; c) providing an alkali metal anode comprisingtwo parts; d) joining said anode parts to corresponding ones of saidelectrode wing sections so as to be in contact with and carried therebyand spaced apart by said web section; e) providing a cathode; f) foldingsaid electrode wing sections relative to said web section and towardeach other in a manner to place said anode parts in operative contactwith said cathode to provide an anode-cathode sub-assembly and; g)placing said anode-cathode sub-assembly in said casing in a mannerplacing said electrode web section in contact with said casing toprovide a case negative electrical configuration; and h) sealing saidcasing.
 4. A method according to claim 3, wherein said step of placingsaid anode-cathode sub-assembly in said casing comprises the steps of:a)providing a metal header; b) joining said metal header to said electrodeweb sections; c) inserting said anode-cathode sub-assembly into saidcasing through the open end thereof and so that said header closes saidopen end and contacts said casing.
 5. A method according to claim 4,further including welding said header to said casing so as to seal saidcasing.
 6. A method according to claim 3, wherein said step of placingsaid anode-cathode sub-assembly in said casing comprises:a) shaping saidelectrode web section to conform to the shape of the inner surface ofsaid casing at a location generally opposite said open end of saidcasing; and b) inserting said anode-cathode sub-assembly into saidcasing through the open end thereof and placing said electrode websection in contact with the inner surface of said casing at saidlocation.
 7. A method of making an electrode assembly for an alkalimetal/oxyhalide electrochemical cell having a conductive casing, analkali metal anode, a liquid cathode/electrolyte in operative contactwith said anode, and a cathode current collector, wherein one of saidanode or said cathode current collector is in two parts, said methodcomprising the steps of:a) providing an electrode in the form of aunitary body having a pair of wing-like sections joined by anintermediate section; and b) joining said anode or said cathode currentcollector parts to corresponding ones of said electrode wing sections soas to be in contact with and carried thereby and spaced apart by saidweb section so that said web section can be placed in contact with saidconductive casing to provide a case negative or positive electricalconfiguration depending upon whether said anode or said cathode currentcollector parts are joined to said electrode sections.
 8. A methodaccording to claim 7, further including the step of folding saidelectrode wing sections relative to said web section and toward eachother in a manner to place the parts carried by said wing sections inoperative contact with the other of said anode or said cathode currentcollector parts to provide an anode-cathode sub-assembly.